Load distributing arrangement between direct-current machines



Sept. 5, 1950 GEORGES-GABRIEL MOZZANINI E lAL 2,521,182

LOAD DISTRXBUTING ARRANGEMENT BETWEEN DIRECT CURRENT MACHINES Filed April 4, 1947 2 Sheets-Sheet l INVENTQRS G rges Grabv-iel Mozzahiui Maurice Lekevfre ATTORNE Sept. 5, 1950 GEORGES-GABRIEL MOZZANINI ET AL 2,521,182

LOAD DISTRIBUTING ARRANGEMENT BETWEEN DIRECT CURRENT MACHINES Filed April 4, 1947 2 Sheets-Sheet 2 Baovqes Gabriel Mozzanm'a and Maurine Lebm've mvEmioRs Thaw Afiomelj Patented Sept. 5, 1950 ."LOADT DISTRIBUTING ARRANGEMENT BE- TWEEN DIRECT- CURRENT MAGHINES Georges-Gabriel Mozzanini, La Garenne C- loinbes, and Maurice Lebertre, PariaFrance Application April 4, 1947,.SerialNo..739,- 180 In France April .6, v1.946

13 Claims.

.various manners.

Our invention has for its chief object an easy .means of .producingastrong torque when start- ...ing andthen the passage from series coupling to parallel.coupling together with, in the case of a group .of'four. motors, a; passage through the inter- .mediary series-paralle1-c0up1ing, each coupling .being associated with the operation of the energizing rheostat ofthe .motors of the group.

Our inventionaimsalso at producing in an auxiliary manner a continuous variation of the z-spee'dof the group of motors.

.According tothe. present invention as applicable .to ..the-. gro.up .or motors, the additiveand. sub- ..tractivewindings.providedin our ,prior form of execution are connected in a manner such that they mayall actas additive windings during the starting period in order to produce a strong torque.

.In its .broad-.concept the.invention relates to a -means. for-controlling .thespeed. of a'direct cur- ..rent.m.otor utilizingin addition to .the .field ex- ..citation winding .a compensating seriesTfie-ldwind- Ling 'which is. arranged to be .connected soas to be additive to the'field flux pro'duce'd 'by the, field .exoitation winding upon starting of the motor .and-thereafter. is. adapted. to be reconnected inthe series circuit: so as to .be subtractive thereby'to weakenthefield .flu-x and to .increasethe. speed of the motor. .In one...aspect.this compensating series field windinglinitialiy. may be. connected. to fbead'ditive and thenmay be short-circuited so as'to reduce the a'dditivefilux thereby to increase .thespeed ottheinotor. In another aspect comtplementary. to. the, preceding aspect'the. resistance of the circuit ,iof the series ffield (winding. andthe (armature-isreduced concomitantly with the reductioncf the l'fiux. .In'the third. aspect .Where .thecompensating series T'fiel'd winding .is con- .nectedto be subtractive..sti.ll further'to reduce the-flux an'dincrease the speed, the. resistance .of

'2 the armature and series field circuit is-still further reduced. Such reductions in the resistance increasing the armature current give further effect to the acceleration of the speed of the motor.

In a-particularform of exdcutiomwe will-place the subtractive series windings forming the compensation winding for each motor between starting resistances inserted in series and-when the starting period is atan end we connect directly on one hand theentrance to the said'resistance tolthe exit of said Winding and 'onthe other hand the exit of the otherresistance to the entrance to said winding.

.In'the case of motors having a shunt or independent field excitation characteristic, which are to'be coupled in .succession'in'series,'in parallel ,or even in seriesmarallel connection-"when there are atleast iiour of such .motors, the "additive windings are connected in a manner such that they maybe switched out of circuit when the motors arecouple'din series.

Other features and advantages of 'our' invention will appear in the'following description and accompanying drawingagiven out, howeverysolely by way. of example.

In said drawings:

Fig.1 is awiring. diagram including two motors with an independent "excitation "connected inaccordance with our invention.

lT'ig. 2 is a diagram: including the automatic control circuit for the same.

.Lastly, Fig. 3 .is awiring "diagram including two motors with a. compound characteristic, the control of which is provide'd with a hand actuated controller or combinator.

Referring'to Figl, Ai an'dBi are'the arma- :tures of two .motors with an independent field excitation, the field coils of which are shown respectively at SSAi and .335; the compensating windings are shownat fiat andfibi inthe case of theadditive windings and at 6b! and Tia! for the subtractive windings. To either side of these latter windings are located starting resistances Ha, Hi1, 52a, 12b, it is apparentthat each of .these two subtractive windings is'connected in series With twostarting resistances.

.A double pole switch Eta, I31) allows connect- .ing the entranceto the starting resistances la,

across the two starting resistances I la and llb respectively. Similarly the double pole switch l4a, l4b allows connecting the same windings in parallel with the tWo starting resistances l2a and l2b respectively.

Broadly considering first the motor Al, this motor may be started by establishing the connection from the supply line 8 consecutively in series through the resistance llb, the compensating series field winding 6bl arranged to be additive, the resistance l2b and thence (through the corresponding compensating winding and resistances of the motor Bl in the arrangement of Fig. 1) through the armature of the motor Al to the supply line 9. This arrangement provides not only for limitation of the rush of the armature current by the interposition of the resistances llb and l2b but secures a high starting torque by virtue of the additive fiux produced by the compensating series field winding Bbl.

The first step of reconnection for accelerating the speed of the motor is to short-circuit the compensating series field winding 6b'l and one of the resistances, in the particular example described the resistance llb by closing the switch l3b. Such short-circuiting decreases the resistance in the armature circuit and at the same time reduces substantially to zero the field flux of the compensating winding Bb'l. The combined effect of decreasing the total field flux and increasing the armature current gives a strong impetus to increase of speed of the motor. Thereafter, upon closing the switch l4b the compensating series field winding 6b'l becomes connected in parallel with both the resistances in llb and l2b, this winding and these resistances as a group remaining connected in series with the armature Al of the motor with which the compensating winding and its cooperating resistances are associated. It is apparent upon a consideration of the wiring diagram of Fig. 1 that by this reconnection to the parallel arrangement the compensating series field winding Bb'l becomes subtractive. The field flux thereby is further weakened and at the same time the resistance in series with the armature is still further reduced. This concomitant action gives a further strong impetus to the increase of the speed of the motor. Further control of the speed of the motor may be accomplished by regulating the rheostat ID to weaken the field 3Al.

The arrangement in relation to the motor Bl is similar and as shown in Fig. I initially the armatures Al and Bl are connected in series, the changes of the connections of the compensating field windings being accomplished simultaneously by the interconnection of the switches l3a and l3b and of the switches Ma and l4b. When upon opening the switch l9 and closing the switch H the armatures Al and BI are connected in parallel the sequence of operations of the switches l3a, l3b, Ma and Nb again may be developed to produce the steps of impetus to increase the speed of the motors thus connected in parallel. It is to be noted also that in the arrangement of Fig. 1 the primary additive series field windings of the two motors are not connected in circuit until the parallel connection is established. Moreover, it should be noted that the sequence of operation of the switches H and. I9 is such that the switch I? is first closed and then the switch I9 is opened and a bridge connection thus is established in passing from the series connection to the parallel connection.

Two other resistances for transient action la and l 5b are inserted in series respectively with the additive windings Sal and libl. They may be respectively short circuitecl by a double pole switch lGa, lfib and another double pole switch ET is adapted to connect them to the mains 8 and 9 through a general double pole switch l8. Switch ll' when closed provides for the parallel connection of the two motors Al and BI whereas a switch l8 when closed with switch l1 open ensures the series connection between these motors. Lastly a field rheostat l9 allows adjusting the energising current of the motor field windings 3A1 and 3B1.

The operation of the arrangement just described is as follows:

We always start the system when the motors are connected in series i. e. the switch IT is open while the switch I9 is closed. The two double pole switches l3a, l3b and l 4a and l lb are also open. The rheostat lll is set in its short circuiting position so that the two motors are under full field conditions; in such a case the motors are connected in series with reference to one another to their subtractive windings Gal and libl and to, their starting resistances Ila, llb, l2a, l2b. The additive windings are not in circuit at the moment considered since switch I1 is open.

It should also be noticed that the subtractive windings are connected in such a manner that during this short starting period they may act as additive windings. It is apparent from the following disclosure how and when they become subtractive i. e. operate normally as in prior arrangements. The object of their operation as additive windings is to provide a strong starting torque.

The next step in the starting consists in closing the switches l3a, l3b which has for its action to shunt the windings lia'l and fib'l by the resistance I la and l lb respectively through said contact switches l3a. and l3b. This being done, the switches Ma and l lb are then closed so as to connect the second resistances I20. and l2b in parallel respectively with the former resistances and with the windings Gal and 6bl. As apparent from the drawing, the entrance to and exit of the windings Ba'l and 6bl are reversed as the latter are now respectively in parallel with resistances the ohmic value of which is clearly higher than the value of their own resistance. Consequently the compensating windings considered as subtractive in the disclosure do now actually act as such.

In order to increase the speed of the motors the value of the active resistance of the rheostat I0 is increased. If the speed of the motor under full field conditions were N, the series coupling is maintained until the speed of the motor reaches 2N.

The series coupling being a stable one it is of interest to compensate for the drop in voltage occurring through the operation of this coupling,

. which drop in voltage is all the more objectionable when the motors are fed only with a fraction of the normal feed voltage, say one half, if two motors are coupled in series, or one quarter 7 if there are four of them.

operation of the motors while furthering the stability of their speedsv while the load might vary.

When it is desired to .make the speed increase still further the parallel coupling is resorted to by simultaneously returning the rheostat H) to its short circuiting position and reinserting the starting resistances Ila, lib, [2a, [2b, in circuit sothat the windings 6a.! and 6b 'l may again be additive. This passage into parallel coupling is obtained in two steps: the double pole switch 1'! is first closed and the motors are operated at the same time under series and parallel connection in a bridge connection through the transient resistances [5a, l5b according to a known connecting system; but it should be noted in the present case the particular feature that the additive windings 6a'l and 6b'l are now inserted in the circuit. Then the switch I9 is opened and parallel coupling is obtained. Lastly the closing of the double pole switch lfia-l6b= short-circuits the transient resistances l5a and i511. This being done the resistances Ha, l'l b, [2a, l2b are again eliminated by being connected across the corresponding windings Gbl and 6a."! which have therefore become again subtractive. increase the speed in the parallel coupling, it is sufficient to reduce the field of the motor by increasing the resistance of the rheostat Ill. With this parallel coupling it is possible to make the speed increase gradually from 2N to 8N.

Thus we obtain a variation in speed of 1:2 in the series coupling and of 2:8 in the parallel coupling.

In order to reduce the speed the reverse operations should be executed in the reverse sequence.

In the case where it is desired to make the arrangement work directly at a speed which corresponds to parallel coupling, the starting nevertheless is again ensured as in the general case with a series coupling, but it would be of advantage to short-circuit the starting resistances I la, ill), I211, I212 only after the coupling has been changed so as to keep the resistances in the circuit and to make the operation smoother.

The diiierent switches described hereinabove may be controlled by hand. However it seems preferable to provide automatic control as illustrated in Fig. 2 by way of example. Said figure shows a wiring diagram of the control circuit allowing the operation of said switches in the desired sequence. In said figure, we have shown diagrammatically the contactor coils l3, l4, l6, l1, I8, -I 9. controlling the contacts or switches l3a, [3b, 140., Mb, [611, IGb l1, l8", 19' respectively of the diagram shown in Fig. 1 together with the supplementary relay coil 20, controlling contacts 20, 2B", 20', a manual double throw switch 2| and two push buttons for starting and stopping shown respectively at 23m and 23a. The coil it controls in addition to the contacts iii, a contact I8" adapted to shunt the starting push button contacts 23m and a contact 3' inserted in series with the contactor coil I3. The latter in addition to its contacts [30. and I3?) controls a contact piece l3" in series with the coil M. The coil 28 controls a contact 21] in series with the coil H, a contact piece 20 in series with the coil [9 and a contact 20" in series with the coil IS. The latter controls in addition to. the contacts Ito. and I61) 2. contact. [6" in series with the coil l3 and a further contact IS" in series with the contact 2.0 and with the coil [9. The coil l'l controls in addition to the contacts H a contact l'l" adapted to shunt the system, of contacts 20" and I6". Lastly the coil [9 controls in addition In order to 6 to the contact 19' a contact [9" adapted to shunt the contact 2 0" and a contact I'S' inserted in series with the coil I6 and the contact 20. All this control circuit may be fed for instance through a switch 22, from the same mains 8' and 9 that feed the motor system.

The operation of this control circuit of Fig. 2 is as follows: Let it be assumed that switch 22 is open, there is no current in the device which therefore is at rest and all the contacts occupy the position as shown in the drawing.

To set the device ready for operation it is suffici ent to close switch 22. Conta'ctor coil 19 becomes energized since contacts 29" and it" are closed due to coils 2t and it being de-energized. Contact l9" then opens and coil H is de-energi'zed while contact l9 opens, contact 20" already being open.

Contaetor coil i9 is consequently the only one energized. To start the group, the push button 23m is depressed so as to feed the contactcr coil it which eiiects closing of contacts l8, l8" and 18"". When the push button 23m is released, the coil of the contactor l8 continues being fed through its holding contact :8" and the normally closed. switch 23a. The energization of coil 48 brings about the closing of the contact l8' provides for the feeding of the contactor coil. 53 through the double throw switch 21' occupying the upper position for series couling as illustrated in the drawing. The energization of the coil it provides for the closing of the contacts iia and I 3?) and consequently the shunting of the system including the resistance lie and subtractive winding to! on one hand and the shunting of the similar system including the resistance Ill), and the subtractive winding 6bi on the other hand. The encrgization of the coil it produces also the closing of the contact Hi" which ensures the energization of the coil hi; this provides for a connection of the resistances lZa and I2?) respectively in parallel with the winding Ea'l and tbl due to the closing of contacts Mia and l lb. It is apparent that this connection eiiects a reversal of current through the windings liai and Sbl. The series coupling is now obtained and it is possible to increase the speed of the motors preferably from I to 2, by adjusting the field rheostat it).

It should be noticed that for series motor coupling the contactor coil 9 is energized because switch 24 being in its upper position, coil 29- is not energized. Contact 20" is therefore closed, contact 23 open, coil Hi d'e-energized and contact it" closed. Coil i9 is energized through closed contacts 2%?" and it" and consequently the auxiliary contacts l9" and it are open. Contactor coil l'i is de-energized and contacts ll open. When it is desired to pass from series couto parallel coupling, it is necessary to re turn the rheostat it to full field conditions and to simultaneously depress the double throw switch 2i. This provides for the deenergization of the contactor coil is, which causes contact I3 to open and coil i l to be ale-energized. This results in a series connection of the starting resistances iia-i2a on one hand and lbl2b on other hand respectively with the windings ta'l' and Eib'i. The result is a reversal of the current in the coils tal and 6b! which are now again additive. At the same time the coil of the contactor 25 is energised, whereby the contact is closed while the contact 25 is opened and the contact'Zd closed. The closing of the contact it" produces the energization of coil I"! and therefore the closing of the contacts H which ensures the bridge connection. The contact l'l" opens and consequently the contactor coil 19 is no longer fed and the contact at 19' opens thus interrupting the series connection of the two motors. The contact l9 closes which allows the feeding of the coil l6 causing the transient resistances l5a and l5b to be short-circuited by contacts Ilia and lBb respectively.

The windings Gal and Sbl are now in circuit. The energization of the coil l6 also closes the contacts l8 which results in the energization of the contactor coil l3 providing through the contacts l3a and [3b for the paralleling of the resistances lla and llb with the windings 6al and Sbl.

Due to the closing of the contact Hi the coil M is now energized, contacts Ma and Mb close and the resistances lZa and I2?) are connected across the windings Eia'l and Bbl respectively.

The parallel coupling is thus ensured and the stability of operation of the two motors is provided through the compensating coils Ga'l and 6b l, the current through which is again reversed and produces a subtractive flux compensating exactly the flux of the additive windings Gal and Bbl when equilibrium is obtained.

A 1:4 variation in speed may now be obtained through operation of the field rheostat ID. The total variation in speed may thus reach a ratio of 1:8, the series coupling providing a variation of 1: and the parallel coupling a variation of 2:8.

Conversely when it is desired to reduce the speed, the field rheostat i is first returned to its position of minimum resistance and the series coupling is then resumed.

The series coupling is obtained by lifting the double throw switch H to the upper position in Fig. 2, the slider of the rheostat l0 being positioned at the point corresponding to the same motor speed for series coupling.

After lifting of the switch H, the coil of the contactor l3 becomes energised through closed contact l8 and the contacts l3a and l3b close. Contact l3 also closes .thus energizing coil l4 and closing contacts Ma. and Mb. The relay coil 28 is simultaneously deenergized causing opening of the contact 20" and the closing of the contact 29". out of the circuit so as to allow the re-insertion of the transient resistances I50, and l5b by the opening of contacts lBa and I617. The contact switch l5" closes and energizes the coil is which ensures through the agency of its principal contact IS the passage into the intermediary bridge connection already referred to and also the switching off of coil l'l, through the opening of contact ES. The contacts ll' open and break the bridge connection and de-energise the additive coils Sc! and fibl. The series coupling is now completed and it is again possible to reduce the speed by adjustment of the field rheostat l0.

At every moment it is possible to operate the stop push button 230. for cutting off the general supply to the motor through the double pole contactor switch l8 the coil l8 of which is decnergized by the opening of switch 23a and this leads moreover to the opening of the contact l 8" and consequently to a de-energisation of the contactor it which opens the contact l3 and consequently de-energises the contactor Hi. All the contacts thus resume their original positions.

It is preferable to start with a series motor coupling even if it is desired to make use of a The relay coil I6 is switched 8 final speed corresponding. to parallel coupling and to this end the double throw switch 2| is set in its series coupling position before-depressing the starting push button 23m. However, if

it is desired to reach very rapidly a speed corresponding to a parallel coupling it is possible to depress the push button 23m and to leavethe switch 2| in its parallel coupling position. In

this case, the elimination of the starting resistances Ila, llb, l2a, .l2b and consequently the reversal of the direction of the current in the windings Eal and eb'l is obtained only after energisation of the contactor coil l6. which allows through auxiliary contact Hi the energization.

of the contactor l3 and then the contactor ll the contacts l 3a, l3b, I la, Nb of which short circuit the starting resistances.

In the preceding example the motors have shunt characteristics and consequently a substantially constant speed whatever their load may be and consequently this type of control is thus practically suitable to the control of machine-tools.

On the other hand in the case of hoisting machines or traction motors, for instance, it is necessary to obtain high starting torques and the constancy in speed is less important. This is the reason why for such application we prefer using compound or series motors the speed of which depends on the torque required.

Referring now to Fig. 3 it is apparent-that Al and BI form the armatures of two motors with a separate excitation the field coils of which are shown respectively as 3Al and 2A2. The additive windings are indicated at Gal and Bbl and the subtractive compensating windings are shown at 6a! and Ebl. The additive windings are coupled in such a manner that they may always be predominant with reference to the subtractive windings whereby the motor may retain a compound characteristic. To either side of the subtractive windings 6b! and Eal are connected the starting resistances lla, llb, l2a, and I212. The resistances l5a and l5b form transient resistances having a common terminal respectively with the starting resistances Ho and H17. A controller C allows obtaining as disclosed hereinafter all the sequence required for starting and for passing from series to parallel coupling. This controller is constituted in. conformity with the diagram (Fig. 3) and its different positions are indicated diagrammatically by position marks numbered from zero to 8. A rheostat l0 allows adjusting the energizing current in the field coils 3Al and 3Bl. v p

The operation of the last arrangement which has just been described is as follows:

The field windings 3A! and 3A2 are fed from an independent source and the value of the excitation current is adjusted by the rheostat Hi. The general supply to the armatures of the two motors is ensuredfrom a main line 8 through the agency of the controller C. When the controller is in its zero position the motor is at rest. The controller allows coupling the two armatures in series or in parallel; for series coupling the positions I, 2 and 3 are used and for parallel coupling the positions 5, 6, l and 8. The position 4 corresponds to a transient position which we may term bridge connection allowing the passage from parallel coupling to series coupling and reversely without breaking the circuit. For starting the motors, we first short-circuit the rheostat l0 and. the controller is then brought to the position I. l

Position 1.-Th'e two armatures are connected in series with the four windings Gal, dbl, and -6a'l, Bb'l and with the. four starting resistances Ha, lib, [2a and i217; this forms the first starting step. The two windings 6a! and EM form additive windings for all the positions of the controller but, in contradistinction, the windings fial and Eb'l are arranged so as to he additive for this first position of the controller in order to provide a large torque when starting.

' Position 2.-=-The windings 6b! and Gn'i are connected in parallel respectively with the resistances lib and Na. The starting continues at a somewhat greaterspeed.

Position 3.'The resistances 12b and lib are also connected in parallel now with the windings Bb'l and So I. As the ohmic resistance of these windings is lower than the ohmic resistance of the starting resistances even when connected in parallel, the windings 6bl and fid'l are fed by a current flowing in a direction opposed to that of itsfiow for positions I and 2. These windings produce a subtractive fiux with reference to the windings Sal-45M which in their turn are additivev with reference to the shunt windings 3A! and 3A2. The position .3 corresponds to the end of the starting period in a series coupling and may be a permanent position whereas the positiens i and 2 are only transient positions. It is then possible to modify the speed of the'motor preferably in a 1:2 ratio by the operation of the field rheostat in. If it is desired to make the motor rotate at a higher speed it is necessary to provide for parallel coupling and to this end tov move the controller on to its next position after previously returning the rheostat into its short-circuit position.

Position 4.-"-This position is only a transient position and allows passing as disclosed from series coupling to parallel coupling or reversely without breaking the circuit. The starting resistances :Hw-Hb, I20 and 1222 are reinserted for operation as in the case of position I. The windings .Bb'l and 6a! are thus fed again with current producing an additive flux. Furthermore a second feed through the wires 8 and 9 connects the transient resistances Mia and [b in the circuit so as to obtain at the same time a series coupling feed through the diiterent starting resistances and a parallel coupling. feed through the different transient resistances just mentioned. The'passage through said position corresponds to the bridge connectionalready described.

Position 5 .--The series coupling is eliminated.

Position (ii-"The two transient resistances I5a and IE1) are eliminated through short circuiting thereof.

The positions 7 and 8 are similar to the positions 2 and ,3 in the series coupling by reason of the .fact that the position 1 allows connecting resistances l to and I la in parallel with the windings fib'l andfia respectively while in positionil the resistances no and I20. are also connected in parallel with said windings so as to reverse the direction of the current in said windings.

Thus two motors are now available the armature-circuits of which include each an additive winding and a. subtractive winding. This position8 may thus be a permanent parallel coupling position for the motors whose speed may be varied, for instance, in a 2:8 ratio by adjustment of field rheostat l0.

It is apparent that by connecting the motors and resistances in this manner it is po sible to obtain in a continuous range a speed variationoi 10 the motors of 1 :8 with the provision that a speed variation of 1:2 is obtained in the series coupling while a variation in speed in a 2:8 ratio is obtained in the parallel coupling.

We may also make use of an arrangement quite similar to those described hereinabove in the case where a double pair of motors instead of a single pair is to be considered as in the preceding case. We would then have to provide simply a supplementary coupling in this case, namely a series parallel coupling.

What we claim is:

1. In a direct current motor drive, the combination with a direct current motor having a field excitation winding adapted to be energized to develop the field flux in a predetermined dir ction, of a compensating series field winding, a resistance, means for connecting said compensating series field winding so as to be additive with respect to said field fiux and in series with said resistance, and means for reconnecting said compensating series field winding so as to be subtractive with respect to said field flux and with said resistance connected in parallel therewith.

2. In a direct current motor drive, the combination with a direct current motor having a field excitation winding adapted to be energized to develop the field flux in a predetermined direction, of a compensating series field winding, a predetermined resistance, an auxiliary resistance, means for initially connecting said com pensating series field winding so as to be additive with respect to said field fiux and in series with said predetermined resistance and said auxiliary resistance and in series with the armature of said motor to produce a limited additive field and to limit the armature current for starting of said motor, means for short-circuiting said compen sating series field winding and said auxiliary re sistance in series therewith to reduce the addi* tive field while maintaining said predetermined resistance in circuit to limit the armature cur rent for acceleration of the motor, andmeans for reconnecting said compensating series field winding so as to be subtractive with respect to said field flux and with said predetermined resistance and said auxiliary resistance in parallel therewith further to reduce the field flux and to provide for anincreased armature current to pro?- duce a desired speed of said motor.

3. In a direct current motor drive, the com bination as defined in claim 2 which comprises a primary additive field winding for said motor, and means for connecting said primary additive field winding in series with said compensating series field winding of said motor.

4;. In a direct current motor drive, the combi nation with a plurality of direct current motors each having a field excitation winding adapted to be energized to develop the field flux of the re spective motors in predetermined directions, of a compensating series field winding for each of said motors, a plurality of predetermined resistances respectively associated with said motors, a plurality of auxiliary resistances respectively associated with said motors, means for initially connecting said compensating series field winding of each motor so as to be additive with respect to said field fiux thereof and in series with said predetermined resistance and said auxiliary resistance associated with said motorand in series with the armature of at least one other motor, means for short-circuiting said compensating sor d inding and said auxiliary resistance in s lrin'l'ewith of each motor to reduce the additive field of said motor while maintaining said predetermined resistance in series with the armature of said other motor, and means for reconnecting said compensating series field winding of each motor so as to be subtractive with respect to said field flux of said motor and with said predetermined resistance and said auxiliary resistance associated therewith in parallel therewith further to reduce said field fiux of said motor and to increase the armature current of said motors.

5. In a direct current motor drive, the combination as defined in claim 4 which comprises means for interrupting the series connection of the armatures of said motor and said other motor, and means for reconnecting said armatures in parallel.

6. In a direct current motor drive, the combination with a, direct current motor having a field excitation winding adapted to be energized to develop the field flux in a predetermined direction, of a compensating series field winding, a pair of resistances connected in series with and respectively at either side of said compensating winding, means for connecting said compensating series field winding and said resistances in series therewith in series with the armature of said motor and so that said compensating series field winding is additive with respect to said field flux, means for short-circuiting said compensating series field winding and one of said resistances in series therewith to reduce said additive field of said compensating series field winding substantially to zero and to reduce the resistance in series with said armature, and means for shortcircuiting said compensating series field winding and the other of said resistances in series 'therewith to connect said compensating series field winding and said resistances in parallel with each other and as a group in series with said armature of said motor and so that said compensating series field winding is subtractive with respect to said field flux and so as further to reduce the resistance in series with said armature.

7. In a direct current motor drive, the combination with a, plurality of direct current motors each having a field excitation winding adapted to be energized to develop the field fiux of the respective motors in predetermined directions, of a compensating series field winding for each of said motors, a pair of resistances associated with each motor and connected in series with and respectively at either side of the respective compensating windings of said motors, means associated with each motor for connecting said compensating series field winding and said resistances in series therewith of each motor in series with the armature of at least one other motor and so that said compensating series field winding of said motor is additive with respect to the field flux thereof, means associated with each motor for short-'circuiting said compensating series field winding and one of the resistances in series therewith of each motor to reduce the additive field of said compensating series field winding of the said motor substantially to zero and to reduce the resistance in series with the armature of said other motor, means associated with each motor for short-circuiting said compensating series field winding and the other of said resistances in series therewith of each motor to connect said compensating series field windin and said resistances of said motor in parallel with each other and as a group in series with the armature of said other motor so that said compensating series field winding of said motor is subtractive with respect to the field flux thereof and so as further to reduce the resistance in series with the armature of said other motor, and means for selectively connecting the armatures of said motors in series and in parallel.

8. In a direct current motor drive, the combination with a plurality of direct current motors each having a field excitation winding adapted to be energized to develop the field fiux of the-respective motors in predetermined directions, of a compensating series field winding for each of said motors, a pair of resistances associated with each motor and connected in series with and respectively at either side of the respective compensating windings of said motors, means associated with each motor for connecting said compensating series field winding and said resistances in series therewith of each motor in series with the armature of at least one other motor and so that said compensating series field winding is additive with respect to the field flux oi the motor with which it is associated, means associated with each motor for short-circuiting said compensating series field winding and one of the resistances in series therewith of each motor to reduce theadditive field of said compensating series field winding of said motor substantially to zero and to reduce the resistance in series with said armature of said other motors, means associated with each motor for shortcircuiting said compensating series field winding and the other of said resistances in series therewith of each motor to connect said compensating series field winding and said resistances of said motor in parallel with each other and as a group in series with the armature of said other motors so that said compensating series field winding of said motor is subtractive with respect to the field flux thereof and so as further to reduce the resistances in series with the arm'atures of said motors, and means for connecting the armatures of said motors in parallel concommitantly with disestablishing said short circuits, said shortcuiting means thereafter being operable to reduce said additive fields and the resistances in series of the said armatures and develop said subtractive fields of the respective motors.

9. In a direct current motor drive, the combination as defined in claim 8 which comprises a primary additive series field winding for each motor, and means for connecting said compensating series field winding and said resistances associated therewith of each motor in series with said primary additive series field winding of said other motor.

10. In a direct current motor drive, the combination with a direct current motor having a 'field excitation winding adapted to be energized to develop the field fiux in a predetermineddirection, of a compensating series field winding, a pair of resistances connected in series with and respectively at either side of said compensating winding, a pair of switches, one of said switches being connected in parallel with said compensating winding and one of said resistances in series therewith and the other of said switches being connected in parallel with said compensating winding and the other of said resistances in series therewith respectively t short-circuit said compensating winding and the respective resistances to change the connection of said compensating winding from said series connection thereot with said resistances to parallel connection thereof with both said resistances and to change said compensating winding from additive to subtractive with respect to said field fiux, a pair of relays respectively operatively connected to said switches to effect operation thereof upon operation of said relays, and means operable successively to operate said relays to effect operation of said switches to effect said short-circuiting of said compensating winding and said resistances.

11. In a direct current motor drive, the combination with a plurality of direct current motors each having a field excitation winding adapted to be energized to develop the field flux of the respective motors in predetermined directions, of a compensating series field winding for each of said motors, a pair of resistances associated with each motor and connected in series with and respectively at either side of the respective compensating windings of said motors, a pair of switches for each motor, one of said switches being connected in parallel with said compensating winding and one of said resistances in series therewith which respectively are associated with said motors, the other of said switches being connected in parallel with said compensating winding and the other of said resistances in series therewith associated with the respective motors, relays operatively connected to the respective switches to effect operation thereof upon operation of said relays, means operable to energize said relays to effect successive closing operation of both of said switches to short-circuit said compensating winding and the respective resistances connected in series therewith to change the connection of said compensating winding and said resistances from series to parallel connection of said compensating winding and both said resistances land to change said compensating winding from additive to subtractive with respect to said field flux, switch means operable selectively to connect the armatures of said motors in series and in parallel, a relay operatively connected to said switch means and to said switch relays to establish said connection of said compensating windings in series with the resistances associated therewith in the respective motors upon establishing the series connection of the armatures of said motors and thereafter to establish said parallel subtractive connection of said compensating series field windings and said resistances, and a relay operatively connected to said switch means and to said switch relays for reestablishing said series connection of said compensating series field windings and the resistances associated therewith of the respective motors upon connection of said motors in parallel and thereafter to establish said parallel connection of said compensating series field windings and said resistances respectively associated therewith of the respective motors.

12. In a, direct current motor drive, the combination with a plurality of direct current motors as defined in claim 4 which comprises means for connecting said armatures in parallel while maintaining said series connection of said armatures, and means for interrupting said series connection of said armatures after connection of said armatures in parallel.

13. In a direct current motor drive, the combination as defined in claim 9 which comprises means for disconnecting said primary additive series field windings when the motors are connected in series.

GEORGES-GABRIEL MOZZANIN I. MAURICE LEBERTRE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,803,676 Powell May 5, 1931 1,953,792 Winne et al Apr. 3, 1934 2,217,432 Cook Aug. 13, 1938 2,403,048 Caldbeck -a July 2, 1946 

